Yamaha RD350 meanderings.

Basic shock mounts added and have started on the bearing carriers on the lathe. It’s harder than ever to pick straight up again with all the distractions recently. Got to get my arse in gear.

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Bearing carriers done, they just need pressing in. Broke out the HSS in the end, which worked perfectly. Cheap insert tooling has been a fucking pain so far.

Tried out my new fly cutter, which I use for decking the top of the cylinder to allow a full size gasket. Worked perfectly!

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Sent up several offerings to the lathe gods last night. I’ve had a problem with intermittent chatter ever since I put it back together. I thought I cracked it shifting to sharper, HSS tools but moving back to steel and I was right back to square one. After trying just about every tool I could find and grinding a few more, I wondered if it might be the spindle bearings on the way out. I stuck an indicator on the chuck and sure enough, there was movement. Turns out, I’d not wound in sufficient preload on the retaining nut. Cuts like butter now and the insert tooling works perfectly. Almost glasslike surface finish on 12L14 steel, even bone dry! Talk about going the long way around….

Some meandering process. I need to recut some 250 cylinder heads I have for the 350 barrels. The involves cutting a new squish band and dome to get the Cc correct. I had to make some sort of radius cutter for the dome part so cracked on with that today. Think it should work pretty well. Just need to grind a tool bit for it.

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Got on with the heads. I made an arbor to hold them in a collet which made keeping everything square a bit easier. I lapped the head on a surface plate then dressed the plug hole on the mill. They’re cut for a bit less than 50% squish area. The target volume was 22cc, which is a bit of a cock to achieve.
There’s not enough meat in the head to cut a single radius dome, so you end up with a series of changing radius, spherical segments. I got relatively close with some calculations, but the last bit required a lot of stopping, and measuring the head volume with a syringe and bit of Perspex.

Not perfect, but I think they should work well…

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Impressive work!

Ta! Quite satisfying that the operation went as planned... (more or less anyways.)

Started work on the porting. I’m trying to throw a few tricks at this one, specifically altering the transfer port walls and b port roof to get them more in the modern school (I.e streams colliding with each other in front of the boost port rather than squirting up the back of the cylinder.)

So far, it’s been bloody fiddly - the castings don’t support wild mods without going through to the head bolt counterbores, or breaking through to clean air outside. I’ve been doing some extremely careful plunging with end miles to rough out the shape, then will clean up and finalize with the hand piece.

For anyone super geeky, the exhaust has been widened close to 70% of bore, not really raised at all. The transfers and boost port will be raised 2mm, reducing the blowdown degrees a bit but giving more transfer time area. The boost port gets widened significantly, and the back wall machined back to a 60 degree angle to fire at the plug….porting always seems to take bloody ages and is nerve wracking.

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More dentist work, lean back in the chair Mr Cylinder, you won't feel a thing.
This worked pleasingly well. I have a little clean up to do as I had to plunge the mill to avoid chatter. Angles worked out perfectly and repeatably though, so not a bad technique I reckon. Easier than a carbide burr. These are the boost ports.

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Think I’m done. I could polish and beautify but I don’t think it will make a massive difference and I have reached CBA max for the moment. Will drop them at the machine shop to get honed to size.

I still need to skim the top face and make a tool to centre them exactly on the heads, after that measure and set the squish. Then pipes, which I have only got as far as printing some paper templates for….Urgh.

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Nicely done - back on the road soon maybe ?

Yeah - I’m rushing now as it needs to be done for mid June.

I do not want to see a bloody pair of aviation snips for a bit. Chopped these out with the Mick Abbey method - a UK tuning guru that is kind enough to put up with my questions…top fella. They are his design too, not all that different from the ones I came up with, but guaranteed these will go better.

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Cut the flat section of the header to make the required bend.

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Vaguely cone shaped….I think I’ll need to machine some tapers to get them round enough.

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Amazing work here. Keep it up!

nice work, ive not done much work with sheet metals like this but it looks very cool

How have I even missed all this. You just boring out heads all night or something

@chak feels a bit that way sometime....

It's always a bit of a disaster to try and hurry this stuff, which is exactly what I'm doing. Anyways, I attempted to get the engine buttoned over the weekend. I doweled the heads to the barrels to try and keep the head perfectly concentric. As standard, they can wander quite a bit which gives you inconsistent squish clearance. Normally, it's 2 holes through the head into the gasket face of the barrel - I tried a different method and it worked ok.

After that, I fly-cut the lip off the top so I could run the full width RD400 gaskets which seal much better and don't distort the heads. At this point, I was all set to bolt it on, and set the squish but to my chagrin discovered that I'd been sent the wrong little end bearings. Boo.

Then I set about pulling off the clutch and primary pinion gears, to change to the 350 ratios. I actually was planning to use a basket and some parts from an old YZ400C MX bike, which has the same ratio, but straight cut gears. On closer inspection though, there is a little damage to the face of one of the teeth on the basket and the idler gear that goes on the back for the kickstart still hasn't arrived. Clutch shelved for now.

So finally, I started welding some of the seams on the cones....not easy! There's only .2mm difference between 20 and 22ga (.98 to .78) but it really makes it harder to weld. I was running just a dribble of acetylene out of my smallest tip and even then, you can't hang around. As is typical, I got my eye in a bit better after the first couple, so I might go back and remake any slightly blobby ones. In keeping with the rest of my efforts this weekend, just as it all started going well, I ran out of O2....

Ho hum.

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Engine is sort of back together - I ended up using a mishmash of 250 and 350 parts for the clutch, keeping the helical gears (and autolube.) Typically, as soon as I put the cover back on and rolled it over on the kickstart a couple of times, the kick start locked up….so will have to pull the bloody cover off again. Set squish at a safe .95mm, it could be a little tighter.

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Phenomenal progress, tough break with the clutch.

May I suggest photos of the progress with your dog in the background?

Got one pipe to fit. I’m getting there with the other. They’re not the prettiest, I could really use some thinner filler, 1/16 is a bit blobby. Ah well…. In theory, these should be all no-filler joints, but getting the fit that perfect would require some sort of taper form tool which I don’t have time for.

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This is going to be on the loud side. Great work !

Haha - it would be ear splitting! I haven’t made the stingers and silencers yet.

Ugly but they fit. The other one needed an extra tweak to clear the sidestand boss. They are a bit blobby but I made them so much quicker than the first set last year. Much of the ugly could be ameliorated by ordering some thinner filler rod, the fit wasn’t that bad for the most part.

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